The present invention relates to a switching-type intake pipe for internal combustion engines.
Switching-type intake pipes are used to improve the filling of the cylinder spaces with combustion air. This is realized by adapting the effective intake pipe length to the engine speed. While a long intake pipe leads to good charging in the lower speed range, the same applies to a short intake pipe at high speeds. To be able to adapt the intake pipe length to the engine speed in a simple manner, switching-type intake pipes having a shorting aperture are used. Said shorting aperture is provided at the cylinder-side end of the intake duct and can be closed and opened by a switching flap. By opening and closing said switching flap the effective length of the intake pipe can be reduced or increased and thus adapted to the engine speed. In the case of a rigid connection of the switching flap with a flap lever there is the danger of the shorting aperture not being capable of being completely closed on its closing seat when the switching flap is only slightly tilted and/or canted. From DE 197 14 311 a switching-type intake pipe is known where the switching flap is fastened via a ball-and-socket joint to the flap lever such that said flap is tiltable within narrow limits. The ball-and-socket joint is formed by a spherical part a in a corresponding hollow space. Said spherical part comprises a narrow neck which is susceptible to break. Further, the spherical part and the corresponding hollow space of the counterpart are difficult to manufacture.
It is an object of the present invention to provide a simple and non-rigid connection of the flap lever with the switching flap.
In the switching-type intake pipe according to the present invention the connection between the flap lever and the switching flap is formed by a plate on the one side and a calotte on the other side via which, in the closing position of the switching flap, the closing force is transmitted, at each tilting angle, from the flap lever to the switching flap. Said plate/calotte assembly only serves for transmitting pressure forces from the flap lever to the switching flap, but not for retaining the switching flap at the flap lever.
The convex calotte occupies a solid angle of less than 180xc2x0 and does thus not comprise any constriction weakening the strength of fastening the calotte to the switching flap or the flap lever. Since the calotte is fastened to the switching flap and/or the flap lever without any undercuts being present, manufacture of said calotte is easy and inexpensive. The same applies to the counterpart of the calotte, namely the plate, which is of flat configuration or, at most, of concave configuration with a large radius. The plate, too, can be inexpensively manufactured with simple means. The calotte and the plate must not be of particularly accurate configuration to ensure good tiltability of the switching flap with respect to the flap lever. The tiltabilty makes sure that the switching flap can position itself gap-free onto the aperture seat of the shorting aperture. This ensures that the shorting aperture can be completely closed such that no undesired short-circuit occurs.
According to a preferred aspect of the present invention the switching flap comprises the calotte, and the the flap lever comprises the plate. Generally, it is also possible that the switching flap comprises the plate, and the flap lever comprises the calotte.
According to a preferred aspect of the present invention the calotte is arranged approximately in the areal gravity center of the switching flap. This ensures that the closing force is applied by the flap lever to approximately the middle of the switching flap. Thus approximately the same pressure is applied to the overall circumference of the closing seat such that a good sealing effect is attained over the overall circumference.
According to a preferred aspect of the present invention the calotte is integrally formed with the switching flap. Separate manufacture of a connecting part and subsequent assembly with the switching flap are thus not necessary.
Preferably, the height of the calotte is selected such that the tilting angle of the switching flap amounts to at least 1.0xc2x0 in each direction. This ensures that unevennesses of the closing seat or changes in the position of the switching flap and/or the shorting aperture occurring during assembly and/or caused by heat can be compensated for.
According to a preferred aspect of the present invention the switching flap comprises an insertion pocket containing the calotte, into which pocket the flap-lever plate is inserted. Via the calotte and the opposite plate only pressure forces can be transmitted. To retain the switching flap at the flap lever and to allow simple assembly, the switching flap thus comprises the insertion pocket on its rear side, in which pocket the plate attached to the flap lever is inserted. For attaching the switching flap to the flap lever, the flap-lever plate is simply inserted into the insertion pocket of the switching flap and prevented from undesiredly falling off the flap-lever plate by means of a snapping or fasting means. This allows simple assembly and/or disassembly.
According to a preferred aspect of the present invention an elastic tensioning element is arranged between the rear side of the plate and an insertion pocket wall. Said tensioning element may be a simple elastic pressure body which presses the flap-lever plate against the calotte of the switching flap. Further, the tensioning element clamps the flap-lever plate in place in the insertion pocket such the flap-lever plate is prevented from undesiredly slipping out of the insertion pocket.